I always put promo credits in for everything I use. I even used to put promo credits for poses, until my pose library grew so big that I will now copy a pose from another project and no longer remember where it came from...

There is no rule, and I don't think there should be. It should be up to each vendor whether they choose to be generous and advertise for other vendors. I think it is good practice, but that is all it is. The fact that customers dislike the lack of promo credits and really appreciate them is something a vendor might want to consider. I certainly do.

Why not send the vendor in question a polite message, asking what products they used? I am sure a lot of vendors will reply. :)

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